This section is intended to introduce various ideas of art that may be related to portions of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing background information to facilitate a better understanding of the various embodiments of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
This disclosure relates generally to methods and apparatus for Downhole Fluid Analysis (DFA). DFA is used to provide information in-situ about the properties of subterranean formations and/or the compositions of reservoir fluids, while the tool is still deployed. Such information can be used to improve or optimize the effectiveness of formation testing tool operations during various sampling processes in a given well, including sampling processes which monitor the effluent from the formation but don't necessarily return a captured formation fluid sample to the Earth's surface. The use of DFA allows for reducing and/or optimizing the number of samples captured and brought back to the surface for further detailed analysis. In addition, DFA can also provide real time information on the status of cleaning operations for a wellbore, among other uses.
Contaminants are often introduced into a well as a result of a drilling process. For example, to facilitate drilling a drilling mud is introduced into the well as a lubricant to reduce the effects of friction between a drill bit and the formation. Consequently, contamination of formation fluid may occur when a filtrate of the drilling mud permeates the formation walls during and after drilling. When drawing formation fluid samples in order to measure the formation fluid quality, the formation fluid samples will often contain a mixture of formation fluid and this mud filtrate. The amount of mud filtrate in a formation fluid sample contaminates the formation fluid and makes it difficult to accurately or precisely determine formation fluid (or hydrocarbon, oil, etc.) composition.
As will become apparent from the following description and discussion, the present disclosure provides methods and apparatus for estimating formation fluid composition that is capable of operating in downhole applications.